Hydraulic system comprising pressure-controlled damping means

ABSTRACT

Hydraulic systems generally comprise expansion hose lines and other damping elements which are provided with one or several serially connected hose chambers according to the generated pressure pulsation. The damping measures of the inventive hydraulic system are initiated according to the prevailing pressure during operation thereof. The aim of the invention is to keep the loss of pressure low and save a significant amount of energy during continuous operations. Said aim is achieved by a direct line connection between the source of pressure and the user, which bypasses the dampers. Said bypass line is blocked by a valve when the pressure in the system increases.

RELATED APPLICATIONS

This application claims priority to international patent applicationnumbers PCT/DE03/01455, filed on May 7, 2003; and DE 102 21 276.7, filedon May 14, 2002, the disclosure of which is incorporated by referenceherein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a pressurized fluid power transmission systemsuch as, for example, a hydraulic system and its damping device.

2. Description of the Related Art

In power transmission systems which use a compressible or incompressiblepressurized fluid for power transmission, i.e., in pneumatic systems orhydraulic systems, pulsation dampers are frequently interposed betweenthe pressure source and the load, said dampers damping pulsations due tothe pressure source or the user. Such pulsation dampers are, forexample, expansion hoses which, in addition, may contain installed inthem, for example, resonator pipes or reflectors for the generation ofpressure wave interferences to extinguish such pressure waves. Suchdamping devices are interposed between the pressure source and the user.

Pressurized fluid power transmission systems are frequently used insituations in which the load varies, i.e., is not constant in terms oftime. Likewise, the pumping rate of the pressure source may fluctuate asa function of the speed of the engine, for example.

Damping devices exhibit a specific resistance to flow which may lead toenergy losses in the power transmission system. These losses are ofconsequence from the viewpoint of economic efficiency. On the otherhand, damping devices cannot just be omitted.

In addition, damping devices frequently are effective only for a more orless wide band of pressure pulsations. If all pressure pulsationsoccurring in every conceivable state of operation are to be eliminatedby the damping device, a complex damping device with correspondinglyhigh resistance to flow is the result.

Considering this, the problem to be solved by the invention is toprovide a pressurized fluid power transmission system, which works veryefficiently and reduces pressure pulsations to a tolerable minimum.

This problem has been solved with the power transmission system using apressurized fluid as disclosed by Claim 1:

SUMMARY OF THE INVENTION

A power transmission system using a pressurized fluid is provided. In anembodiment, the inventive pressurized fluid power transmission system isconfigured as a hydraulic system. This system comprises a pressuresource and a load, between which a damping device is arranged. Thisdevice comprises at least two channels which are arranged parallel withrespect to each other and exhibit different damping properties. Forexample, one of the channels comprises one or more pulsation damperswhile the other channel comprises differently tuned pulsation dampers,or may even be configured as a bypass channel which does not compriseany pulsation dampers or other dampers. The channels are associated witha valve means which effects the pressure distribution to the channels asa function of the pressure applied to one selected point of the dampingdevice. As a result, at least one of the channels is activated in apressure-dependent manner, i.e., opened or closed, or even more or lessopened. Consequently, the properties of the damping device vary,depending on the pressure at a selected site of the power transmissionsystem. As a result, it is possible to work on the one hand with agreater damping effect in certain states of operation of the powertransmission system and on the other hand with a lesser damping effectin certain other states of operation. In conjunction with the change ofthe damping effect, there usually is a change of the flow resistanceprovided by the damping device, consequently, it is possible, inaccordance with the inventive power transmission system, to adapt theflow resistance provided by the damping device to the states ofoperation of the power transmission systems, i.e., in particular, to theload ratios. For example, the power transmission system may be used as ahydraulic system in motor vehicles. In straight-line driving mode, whichdoes not require any steering assistance, a channel provided in thedamping device and acting as a bypass may be opened. The powertransmission system is in recirculating mode, so that in this instancedamping is not important. However, the reduced flow resistance in thebypass channel in this operating state requires only little power inorder to maintain the recirculating mode, so that only a small load isapplied by the hydraulic pump (pressure source) to the engine of themotor vehicle.

When a steering action is initiated, the flow resistance of thehydraulic actuator device—which is used for steeringassistance—increases. Corresponding thereto, the pressure in or at thedamping device increases. This pressure causes the valve means to switchpreferably suddenly or, if needed, also in a sliding manner, so that thebypass channel or another channel with low flow resistance used duringrecirculating mode is now increasingly throttled. Now, increasingly,fluid is forced to flow through the parallel channel which contains atleast one pulsation damper. In doing so, pulsations, pressure shocks,and vibrations, which could be caused by the pressure source, are keptaway from the load. Conversely, pulsations, vibrations, and pressureshocks which can originate from the load, are kept away from thepressure source. Consequently, any power losses which could occur at thedampers of the damping devices are largely restricted to brieflyoccurring steering actions. A hydraulic level control may occur in asimilar manner.

Consequently, the inventive power transmission system activates itsdampers only when a power transmission actually occurs between thepressure source and the load In idling mode (recirculating mode), i.e.,when no appreciable power is transmitted from the pressure source to theload, the dampers—which inevitably involve energy losses—are at leastpartially deactivated.

Furthermore, the inventive power transmission system permits the use ofthe pulsation dampers, mainly when pulsations actually do occur. This isa function of load, for example. In addition, the frequency spectrum ofthe pulsations may change in response to the load. Also, in this case,the inventive power transmission system offers the option of activatingor deactivating the pulsation damper adapted for specific pulsations asa function of the operating state of the power transmission system.

The damping device may have two or more channels arranged parallel toeach other. They may be connected with each other on their respectiveinput sides and switched on their output sides, or they may be connectedwith each other on their output sides and switched on their input sides.This switching operation may be performed by bypass valves. However, inpreferred embodiments, the channel to be deactivated only contains ashut-off valve which closes when the pressure increases, for example.This shut-off valve is preferably arranged in that one of the twochannels which exhibits the lower flow resistance. This channel may beconsidered as the bypass channel which, for example, is graduallyblocked as the pressure of the system is increased.

For example, as mentioned, it is basically possible to activate ordeactivate the channels in a surge-like manner. This, however, mayresult in a noticeable change of the behavior of the overall system. Forexample, considering a motor vehicle steering system using hydraulicassistance, the degree of steering assistance would change suddenly. Inthose cases, a smooth transition between activated and deactivatedchannel is preferred. This sliding mode of operation allows thefading-over or switching between channels, preferably in a manner thatis substantially free of hysteresis effects. In contrast, when a slidingtransition is used, it is advantageous if a certain switching hysteresisexists in order to avoid vibration conditions, i.e., in order to avoid aconstant hunting of the valve means certain states.

In order to switch the valve means, the valve actuating pressure ispreferably drawn from the damping device or another point of the powertransmission system. By means of a suitable pressure-activated drivingarrangement, the pressure may be used for moving the valve means.Preferably, the actuation arrangement comprises a spring means whichgenerates a counter-force. In many cases, it is sufficient if the springmeans exhibits a linear force-versus-path characteristic. In individualcases, it may be useful if a nonlinear force-versus-path characteristicis provided. This allows compensation of a non-linear valvecharacteristic. In other cases, it may even be desirable to employ anon-linear characteristic for switching between the two channels.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional details of advantageous embodiments of the invention areobvious from the drawings, the specification or the subclaims.

FIG. 1 is a schematic illustration of an invention pressurized fluidpower transmission system and

FIGS. 2–5 are schematic illustrations of modified forms of embodimentsof inventive power transmission systems.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a hydraulic system 1 which uses an incompressible fluid,such as for example hydraulic oil, as a pressurized fluid. This means isused for the transmission of the mechanical output of a pressure source2 to a user 3. Consequently, hydraulic system 1 is a pressurized fluidpower transmission system comprising. Pressure source 2, for example, isa hydraulic pump provided on a motor vehicle. Load 3, for example, is asteering gear, a valve block or another actuator to be driven bypressure source 2. A damping device 4 is interposed between pressuresource 2 and load 3. Input 5 of this damping device is connected withone output 6 of pressure source 2. Its output 7 is connected with oneinput 8 of load 3. A recirculating line from the load to pressure source2 is provided, however not illustrated. (This applies to FIGS. 1 through5.)

Damping device 4 contains at least two channels 9, 11, which arearranged parallel to each other. To achieve this, the input sides 12, 13of channels 9, 11, as well as their output sides 14, 15, are connectedwith each other. Channel 9 is configured as a bypass channel and, inthis form of embodiment, does not contain any damping devices or thelike; however, it does contain a shut-off valve 16 which acts as a valvemeans for dividing the hydraulic fluid between channels 9, 11. Shut-offvalve 16, located in the bypass channel (channel 9), has a first stateI, in which it is fully open and enables channel 9, and a second stateII, in which it blocks channel 9. Furthermore, said valve may adopt anystates in between, in which it more or less throttles channel 9.Shut-off valve 16 is activated by the pressurized fluid. Said valvecomprises a pressurized fluid drive 17 which, when pressure is applied,actuates shut-off valve 16 in closing direction against the force of apressure spring 18. Pressurized fluid drive 17 is connected with input12 of channel 9 by means of a line 19, for example. If desired, e.g., toavoid any switching hysteresis, line 19 may also be connected with thevalve output.

Channel 11 contains at least one damper; however, in this instance itcontains two dampers 21, 22, which are arranged in series. Both dampers21, 22 are pulsation dampers, for example, each comprising an expansionhose and a tuner pipe 23, 24 located in said expansion hose. Each damper21, 22 is adjusted to a specific pulsation frequency or a frequencyband.

The two paralleling channels 9, 11 may be preceded by a joint damper 25which connects the input of damping device 4 with the inputs 12, 13 ofchannels 9, 11. Damper 25 may be a pulsation damper adjusted for narrowor wide bands.

The so far described hydraulic system 1 operates as follows:

During operation, pressure source 2 constantly transports hydraulicfluid. If load 3 does not tap any power, it allows the fluid arriving atits input 8 to pass unimpeded and flow back to pressure source 2 througha not illustrated recirculating line. The hydraulic system operates inrecirculating mode. In this state, the pressure tapped by line 19 is lowin damping device 4. Consequently, shut-off valve 16 is in its state I,i.e., it allows unimpeded passage into channel 9. Consequently, thehydraulic fluid takes its path through damper 25 and then throughchannel 9 which is switched as the bypass to user 3. The flow throughchannel 11, which is also open, is comparatively lower because of thischannel's greater flow resistance. Therefore, in order to maintain thehydraulic circulatory system, pressure source 2 requires only low power.

As explained above, user 3, for example, is a hydraulic actuator whichassists the steering motion of a motor vehicle. If this user isactivated by a steering motion, it offers increasing resistance to thehydraulic fluid which passes through. In doing so, the pressure in thedamping device increases noticeably, specifically at input 12 of channel9. In turn, this pressure triggers the initial closing operation ofshut-off valve 16 by means of pressurized fluid drive 17. Therefore,channel 9 is throttled increasingly, thereby forcing increasingly morefluid to take the path through channel 11 and thus over dampers 21, 22.As a result, it is ensured that the increasing transmission of powercauses the concurrent damping of pulsations between pressure source 2and user 3. If, at maximum counter-pressure, shut-off valve 16 is closedcompletely, channel 9 is shut off.

Then, only channel 11 is active. Operation takes place with fullpulsation damping. The connection between-the pressure tapped at line 19and the fluid distribution to channels 9, 11, can be adjusted byselecting an appropriate force-versus-path characteristic for pressurespring 18.

If load 3 is deactivated, for example, by resetting the steering tostraight-line mode of operation, the hydraulic fluid may again flowunimpeded through load 3. Hence, the pressure tapped by line 19 drops,and channel 9 is cleared as the pressure drops. Consequently, the systemreturns to recirculating operation with low pulsation damping. This is alow-loss operation and, hence, is maintained until load 3 becomes activeagain.

As an alternative, line 19 may lead to output 7 in order to exclude orreduce positive feedback effects. However, this also avoids anyhysteresis which would be desirable to avoid vibrations in some cases.

FIG. 2 shows a modified embodiment of hydraulic system 1. Thisembodiment is different from the above-described embodiment in thatdamper 25 was omitted. This results in an undamped but still extremelyloss-free recirculating operation when channel 9 acting as bypass isleft fully open, i.e., when there is no power decrease to load 3. In asmuch as these embodiments are otherwise completely identical, referenceis made hereinafter to the above description and the application of thesame reference numbers. For example, the number of dampers in channel 11may vary as needed. Valve 16 may be located in or in front of channel 9.

Another potential modification of hydraulic system 1 of FIG. 1 is sownby FIG. 3. Again, full reference is made to the description of theexample of embodiment of FIG. 1. The same reference numbers apply.Different from the example of embodiment of FIG. 1, hydraulic system 1of FIG. 3 comprises only one pulsation damper 21 in channel 11. Its flowresistance is considerably greater than that of open channel 9, so thatthis channel causes a substantially greater pressure drop. Therefore,when channel 9 is open (recirculating operation), only the combinedtotal of the flow resistance of damper 25 and the substantially lowerflow resistance of channel 9 is effective. Consequently, the pressuredrop between pressure source 2 and load 3 is substantially determined bythe pressure drop on damper 25. However, if load 3 removes power,channel 9 is closed more and more, so that damper 21 becomes active. Nowthe pressure drop of damping device 4 is added to the pressure drop ofdamper 21, so that there is an increased pressure drop, but alsoincreased pulsation damping.

FIG. 4 shows another modified form of embodiment of hydraulic system 1.In this form of embodiment, both dampers 25, 21 are bridged by a bypasschannel which is open as long as the system operates in recirculatingmode. Dampers 21, 25, which are actuated only when load 3 requiresmechanical power, may be designed for high pulsation damping effects.Concomitant pressure losses only occur during—as a rule—brief phases ofthe power drop, so that these phases are negligible regarding the energybalance of the system. In contrast, these phases are of no effect inrecirculating mode.

Specifically, damper 21 is part of channel 11. Regarding this channel'sdescription and function, reference is made to the description inconjunction with FIG. 3. The same applies to channel 9. Differenttherefrom, damper 25 forms a channel 11 a which is associated withchannel 9 a. Input 13 a of channel 11 a is connected with input 12 a ofchannel 9 a. Both are located at output 6 a of pressure source 2. Whileoutput 15 a of channel 11 a is connected with inputs 12, 13 of channels9, 13, output 7 a of channel 9 a is connected with output 7 of channel9. Consequently, channel 9 a forms a bypass which bridges damping device4 as a whole. This bypass is controlled by valve 16 a which is connectedwith the output of pressure source 2 via a pressure line 19 a.

This hydraulic system 1 is designed in such a manner that both shut-offvalves 16, 16 a are open in recirculating state. A low pressure dropexists. Pulsation damping does not occur. If load 3 decreases as aresult of a corresponding control of power, a counter-pressure iscreated in hydraulic system 1, whereby this pressure initially causesvalve 16 a to close. As a result, damper 25 is activated increasingly.As the counter-pressure rises, valve 16 is also closed, which now alsocauses damper 21 to be activated. Thus, as power drops more and more,pulsation damping increases correspondingly. In doing so, shut-offvalves 16, 16 a may be dimensioned—by appropriately dimensioningpressure springs 18, 18 a—in such a manner that they successively exerttheir blocking action or that they fix an overlap range in whichshut-off valve 16 begins to close, while shut-off valve 16 a more andmore approaches its completely closed state II.

Also, in this system which permits extremely high pulsation damping,such damping is prompted only during phases of power transmission.Consequently, damping losses that occur will be limited to these briefphases.

An even further modified embodiment of hydraulic system 1 is shown byFIG. 5. Regarding this, reference is made to the same reference numbersand the description of the hydraulic system of FIG. 1. The differencedescribed hereinafter consists in the arrangement and configuration ofthe valve means. As such, a switching valve 26 is provided which,alternately, connects the outputs of channels 9, 11 with load 3. Inaddition, channel 9 is not purely a bypass channel but contains dampingelement 25. It may be omitted, if required. If required, pressure line19 may be connected with input 5 of damping device 4 or with anotherpoint of hydraulic system 1.

Hydraulic systems 1, as a rule, contain expansion hose lines and otherdamping elements 21, 22, which, depending on the generated pressurepulsation, are provided with one or more serially connected hosechambers. These chambers represent the flow resistance, as well as theresilience and inertia features of the system, which result in thedamping of input pressure signals. Frequently, the pulsation of the pumpincreases with static pressure, i.e., for example, with the degree andintensity of the steering operations or with the degree of assistance ofa hydraulically active assistance system. Pulsations may be minimized bydamping measures, as a result of which the pressure loss increases and,hence, the energy loss increases. This situation is remedied by theinvention in that, during the operation of a hydraulic circulatorysystem, the damping measures are activated as a function of pressure. Asa result of this, a minimal pressure loss and considerable energysavings are possible in recirculating mode. This is achieved by a directline connection which is provided between pressure source 2 and user 3,and which bridges the dampers. This short-circuit line is blocked by avalve when a pressure increase occurs in the system. Inasmuch as thepressure loss occurring on the damper occurs only very briefly, dampingelements featuring a strong damping effect and a high pressure loss andhaving an extremely strong damping effect on pressure fluctuations canbe used during these brief periods of time. Still, considering the meantime of activation, an improved energy balance can be achieved.

1. A pressurized fluid power transmission system, comprising: a pressuresource; a load; and a damping device interposed between the pressuresource and the load, the damping device including at least two channelsarranged parallel to each other and having different flow resistances,the channels being controlled by a valve means that affects the flowdistribution to the channels as a function of the pressure at a selectedpoint of the power transmission system by at least partially closing thechannel having a lower flow resistance in response to an increase inpressure sensed at the selected point, wherein at least one of thechannels contains at least one pulsation damper that includes anexpansion hose containing at least one resonator pipe or reflector. 2.The pressurized fluid power transmission system in accordance with claim1, wherein the channel that has a greater flow resistance contains theat least one pulsation damper.
 3. The pressurized fluid powertransmission system in accordance with claim 1, wherein each channel hasone channel input, respectively, and one channel output, respectively,and that the channel inputs are connected with each other, and that thechannel outputs are connected to the valve means.
 4. The pressurizedfluid power transmission system in accordance with claim 1, wherein thevalve means is a switching valve.
 5. The pressurized fluid powertransmission system in accordance with claim 1, wherein the valve meansis configured as a shut-off valve.
 6. The pressurized fluid powertransmission system in accordance with claim 5, wherein the valve means,when opening and closing between the closing state and the openingstate, features a gradual smooth transition.
 7. A pressurized fluidpower transmission system, comprising: a pressure source; a load; and adamping device interposed between the pressure source and the load, thedamping device including at least two channels arranged parallel to eachother and having different flow resistances, the channels beingcontrolled by a switching valve that includes a gradual, slidingtransition when switching between the channels, wherein the switchingvalve affects the flow distribution to the channels as a function of thepressure at a selected point of the power transmission system by atleast partially closing the channel having a lower flow resistance inresponse to an increase in pressure sensed at the selected point,wherein each channel has one channel input respectively, and one channeloutput respectively, and that the channel outputs are connected witheach other, and that the channel inputs are connected with each othervia the switching valve.
 8. A pressurized fluid power transmissionsystem, comprising: a pressure source; a load; and a damping deviceinterposed between the pressure source and the load, the damping deviceincluding at least two channels arranged parallel to each other andhaving different flow resistances, the channels being controlled by avalve means that affects the flow distribution to the channels as afunction of the pressure at a selected point of the power transmissionsystem by at least partially closing the channel having a lower flowresistance in response to an increase in pressure sensed at the selectedpoint, wherein the valve means is connected with a fluid-activatingdevice which actuates the valve means, the fluid-activating devicecontaining a spring means that exhibits a non-linear force-versus-pathcharacteristic to counteract the generated force of actuation.
 9. Thepressurized fluid power transmission system in accordance with claim 8,wherein the fluid-activating device comprises an input line which isconnected with a line leading to the valve means in order to tap thecontrol and actuation pressure.
 10. A pressurized fluid powertransmission system, comprising: a pressure source; a load; and adamping device arranged between the pressure source and the load, thedamping device including at least two channels arranged parallel to eachother, the at least two channels including a first channel and a secondchannel having a greater flow resistance than the first channel, whereinthe second channel includes at least one pulsation damper having anexpansion hose containing at least one resonator pipe or reflector, thechannels being controlled by a valve that affects the flow distributionto the channels as a function of pressure by at least partially closingthe first channel in response to an increase in pressure in the powertransmission system.
 11. The pressurized fluid power transmission systemin accordance with claim 10, wherein the valve is configured as ashut-off valve.
 12. The pressurized fluid power transmission system inaccordance with claim 10, wherein the valve is connected to afluid-activating device that actuates the valve.